The former Ryder Cup star has fallen from fourth in the world to outside the top 130 in the last two years, but was on the leaderboard for much of last week at Congressional. Still wearing a bandage on his finger, Stenson overcame some torrential afternoon downpours to grab an eagle and seven birdies.

"I don't think you will find a player who's been out here 10 to 15 years who has not had some rough times," he said. "We all go through ups and downs. I've been struggling with my game a little bit, but it's hard to put my finger on what it's been.

"I played a lot better last week,” he added. “My confidence is still not as high as it can be, but I'm working away trying to do the things that are going to lead me back."

Boyd tied for second in the BMW Italian Open two weeks ago and, like Rory McIlroy in America, broke 70 in all four rounds.

The 24-year-old, first man off Thursday morning and playing in much the best conditions of the day, grabbed eight birdies and would have finished the round alongside Stenson but for missing the green with a pitch to his final hole and taking a bogey 6.

Compatriot Danny Willett, a teammate of McIlroy at the 2007 Walker Cup, and Scotland's 1999 British Open champion Paul Lawrie had 66s to share third place with South African Jbe Kruger and Dutchman Tim Sluiter.

Two-time U.S. Open champion Retief Goosen is two strokes further back and Sergio Garcia returned a 69, while on his 48th birthday Colin Montgomerie managed a 2-under 70. Alongside last year's Ryder Cup captain are world No. 3 Martin Kaymer, American star Dustin Johnson, defending champion David Horsey and 18-year-old Italian Matteo Manassero.

Montgomerie wasn’t happy about the weather. On the 14th, he was forced to drop his ball out of a puddle in a bunker.

“I’m getting to that stage where I should be spending birthday days on a beach in the Bahamas, and not having to be drenched out here,” he said. “This was a horrific day.”

Paul Casey would have been inside the top 10 but for one hole, the 441-yard seventh. Four under with three to play, he hooked into thick rough, moved the ball only a few yards with his first two hacks at it, went over the fairway, then into a greenside bunker and eventually walked off with a quadruple-bogey 8.

Casey, round in 72, still finished four shots better than 53-year-old Bernhard Langer on his 450th European Tour appearance, while a 14th successive missed cut going back to last November looms large for England's Nick Dougherty after his 75. That contained an eagle and three birdies, but also three bogeys, a triple-bogey 7 and a closing double-bogey 7.

Stenson was among the late starters who had to endure a rainfall that made for higher scoring in the afternoon, but the Swedish star still managed seven birdies and an eagle to go along with a lone bogey. Stenson eagled the par-5 sixth hole to reach the turn in 5 under. He nearly eagled the 18th as well but missed a 4-foot putt and had to settle for a birdie.

“It would have been nice to make that, it would have been even sweeter,” said Stenson, who also chipped in for birdie at the 14th. “I just misjudged it. I tried to go left of center and I didn’t think it would break to the left, but it did. I probably pulled it a bit too.”